The “giant” magnetoresistance (GMR) (Ni80Fe20)O–Co–Cu based “top” spin valves were studied with and without Ni80Fe20 as a seed layer. Microstructure examination shows that without the seed layer, the “free” and the “pinned” Co layers of the spin valves are highly irregular, discontinuous, and connected by pinholes across the Cu spacer layer, resulting in a large coupling >5.96 kA/m (>75 Oe) and a negligible GMR effect (<0.7%). The presence of Ni80Fe20 seed layer leads to continuous layers without pinholes and smooth interfaces in the (Ni80Fe20)O–Co–Cu, thereby essentially eliminating the coupling between the “free” and the “pinned” layers (0.23 kA/m or 2.9 Oe), a more than 25-fold reduction with respect to the seedless spin valves. Reduced detrimental coupling results in more than an order of magnitude increase in GMR (8.5%) in the NiFe seed layer spin valves. Domain studies confirm that the “pinned” and the “free” layers in seedless spin valves reverse their magnetization in an overlapping field range, and independently in spin valves deposited in the presence of a seed layer.
Carbon (in the form of hydrocarbons) is a common contaminant in high and ultra-high-vacuum systems, and easily gets incorporated in films during deposition. This work reports the highly deleterious role of small amounts of carbon on the structure and magnetic properties of “giant” magnetoresistance (GMR) spin valves. Controlled incorporation of 1–3 at. % carbon in Co/Cu layers of NiO–Co–Cu-based spin valves has been found to completely eliminate the GMR effect. Transmission electron microscopy (TEM) shows that carbon promotes highly discontinuous Co/Cu layers, resulting in a large number of pinholes; domain studies corroborate that the “free” layer under the influence of a large pinhole coupling is unable to switch independently of the “pinned” Co layer. These results also have implications for other multilayers and spintronics devices.
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